The second point thing that stands out for Acumbamail compared to mailchimp is the rates. The American service is much more expensive and has fewer pricing plans. This means you have to pay more if their tariffs don't happen to exactly meet your needs.
At Acumbamail you can choose monthly payment plans per subscribers or per number of sent emails. If you want to send a single message we also have a prepaid credit option. Mailchimp does not have payment plants per sent campaigns, they only have prepaid credits or monthly payment plants per subscribers.
Since mailchimp doesn't have payment plants per sent campaigns, it is likely you will end up paying for a higher price plan than you need. For example, if you have 10,000 subscribers and you want to send two campaigns per month, with Acumbamail you can simply opt for the 15-euro per month plan, whereas with mailchimp you will have to sign up for the 10,000 subscriber payment plan, which will cost you 69.32 euros. What are you waiting for to try the Spanish mailchimp?